The method disclosed in Japanese Patent 2572621 is among known techniques pertinent to production of a molded article that generates heat using oxidation reaction of oxidizable metal powder with oxygen in air.
According to the method, a raw material slurry is prepared by suspending a fibrous substance in water and adding thereto an oxidizable metal, e.g., iron powder, activated carbon as a moisture retaining agent, an electrolyte as a reaction promoter, etc. A wet web is prepared from the slurry by a papermaking process, dewatered by suction, and pressed into a heat generating molded article of sheet form having a water content of 5 to 65 wt %.
The heat generating molded article manufactured by the method is as thick as 0.2 to 10 mm. As the oxidation reaction proceeds, it becomes brittle and loses flexibility. Therefore, when applied as, for example, a warming sheet to a bending part of a body, such as an elbow or a knee, with that thickness, it becomes uncomfortable to wear with time. In applications to self-heating containers or keep-warm containers, the molded article has difficulty in closely conforming to some containers. The technique has additional disadvantages such that the molded article has poor fabricability in, e.g., trimming; that oxidation is liable to occur in the slurry by oxygen in the slurry and in air, which can cause reduction of performance and can rust equipment; and that the molded article cannot be taken up in roll, which has been a bar to productivity.
Accordingly, an object of the present invention is to provide a heat generating sheet excellent in not only conformability to a part of a body or a container but fabricability and productivity, a method of producing the heat generating sheet, a molded sheet used in the production of the heat generating sheet, and a method of producing the molded sheet.